Electroacoustical musical instrument



Nov. 8, 1949 c. c. BROWN 2,487,420

ELECTROACOUSTICAL MUSICAL INSTRUMENT Filed Feb. 10, 1947 2 Sheets-Sheet1 Fig. i.

I )1 w nter Charles C. Brown By 2mm Nov. 8, 1949 c. c. BROWN 2,487,420

ELECTROACOUSTICAL MUS ICAL INSTRUMENT Filed Feb. 10, 1947 2 Sheets-Sheet2 I11 vellto r V Charles C. Brown 60 Fig. 5.

II2 y Patented Nov. 8, 1949 ELECTROACOUSTICAL MUSICAL INSTRUMENT CharlesC. Brown, Los Angeles, Calif.

Application February 10, 1947, Serial No. 727,507

6 Claims.

This invention relates to electro-acoustical musical instruments of thepiano or organ type provided with a keyboard on which the keys areoperated or played in the customary fashion, but in which the tones areproduced electro-acoustically.

It is the main object of this invention to provide as compact aninstrument as possible, which may be folded for transport and may becarried by the operator himself, while presenting the appearance andgiving the performance of an ordinary piano.

It is a further object of the invention to substantially improve thosemeans which are producing the electrical oscillations to be convertedinto sound oscillations.

It is a further object of the invention to simplify themechanical meansfor producing oscillations while maintaining as far as possible thecharacter of the tones produced.

It is a further object of the invention to provide means capable ofbeing assembled on a small space in direct vicinity of the keyboard.

It is finally a further object to simplify the conversion of mechanicaloscillations into electrical oscillations and to produce a resultingoscillation capable of being treated with conventional means forproducing the sound picture.

Further objects will be apparent from the following specification.

One embodiment of the invention and several modifications are shown inthe accompanying drawings. It is to be understood however, that saidembodiment and said modifications are to be regarded as examples servingmainly the purpose of explaining the principles on which the inventionis based and that these principles may be incorporated into otherembodiments or modifications some of which have been mentioned orforeshadowed in the following specification. The construction or use ofmodifications and further embodiments based on the principles asexplained is, therefore, not necessarily a departure from the invention.

In the drawings:

Figure 1 is a perspective view of a musical instrument of the pianotype;

Figure 2 is a perspective view of a case serving as a housing for theelectrical equipment and as a case for accommodating the instrumentduring transport;

Figure 3 is a front view of the keyboard chest, when folded;

Figure 4 is a sectional elevational view of the keyboard chestillustrating diagrammatically the 2 apparatus and the electricalconnections which are used.

Figure 5 is a sectional partial view of a modification.

One of the main objects of the invention consists in providing afoldable piano-like instrument which may be moved without difficulty byone man and which does not occupy much space during transport. Thegeneral construction of the instrument is, therefore, shown in Figures 1and 2, illustrating a modification when set up ready for use, whileFigure 3 shows the instrument when folded for transport.

It will be seen that the instrument comprises a keyboard chest it whichis divided into two sections H, H forming separate units connected byhinges R4. The front side of the chest may be provided with a shiftablelock plate 34, and the pin 35. The division of the keyboard chest intoseparate units permits the use of a keyboard 33 of 88 keys as customaryon a piano and on similar instruments.

The chest is supported on feet l5 hinged at Hi to the bottom of thekeyboard chest and braced by means of pivoted brace members H.

The pedals l8, I9, 28 are mounted on a separate block 2! which isconnected with the instrument by means of a cable 22, provided with aplug which is inserted into a suitable connector (not shown) at the backof the chest of the instrument.

The entire electric sound producing equipment is contained in a case 25according to the modification shown in Figures 1 and 2 which issubdivided into two compartments 26, 21 by means of a partition wall 28.The upper compartment 26 in the example shown contains the amplifier,speaker and all other equipment mounted on a suitable base box 38 whichcontains the connections and to which cables 29, 30 with suitable plugconnectors 3!, 32 are leading. One of these plug connectors is insertedinto a socket provided on the keyboard chest, for connection with thoseunits which are associated with the key, while the second cable 30 isconnected with the mains or with the available source of supply current.

The amplifier and speaker box 38 and case 25 are preferably placed intoa position which is suitable with respect to the acoustic effect, eitherbelow or above the instrument or at some other suitable place. An outlet(not shown) may be provided for connection with a public addresssystern.

When folded for transport the two chest sections which may be locked, ifnecessary, form a single box as shown in Figure 3 which may be insertedinto the lower compartment 21. Suitable guiding ledges 39 may beprovided for this purpose. The space between the guiding ledges may beused for storing smaller parts such as the pedal block and the like.

The keyboard chest l essentially comprises a closed portion 4| and anopen section 42 and contains either that part of the electro-acousticequipment which is associated with the keys or as shown in Figure 4,practically all of said equipment.

Section 4| ends in a stepped portion or border ledge 43 on the side ofthe keyboard which reaches down towards the keys Ml which are pivoted at44 on a lug 45 depending from the top board of section 4|. White andblack keys are treated alike as regards the connection with the soundproducing mechanism, merely the location of the upper surface and thelength of the projecting part on the board being changed in thecustomary way.

The front section 46 of the keys covers the open section 42 of the chestcompletely, so that the keyboard is an exact replica of a pianokeyboard. The front wall 48 may form or hold a stop bar 47 for the keys.

The rear section of the keys actuates a damping mechanism to bedescribed below.

In the space below the keys the electro-acoustic tone production deviceis located which is mounted on a supporting board 52 held on a highlycompressible and yieldable layer 53 preferably made of sponge rubber, orof other shock absorbing non-oscillating material. The board and theshock and oscillation absorbing compressible elastic layer may be fixedto the bottom board 54 of the chest In in any desired manner either bymeans of glue or cement or by mechanical means. It is, however, to beunderstood that the electro-acoustic tone producingv and dampingmechanism is fixed on the supporting board 52 and not to the bottomboard 54 so that shocks or oscillations imparted to the mechanism arenot transmitted to the bottom board. No reaction is, therefore, producedwhich might interfere with the production of sound oscillation.

The supporting board carries uprights 5B, 58 of wood or metal below eachkey fixed by mechanical means such as screws, and projecting toward thekeys. The uprights 56 form a series,

one upright or a pair being arranged below each key. The uprights 58 mayeither be separate units arranged below each key or instead of such aseries a cross bar (as shown in Figure 4) mounted transversely withrespect to the keys may be arranged. This cross bar 58 carries a tuningfork .60 for each key which is fixed thereon by means of a stem at theclosed end of the tuning fork which passes through a hole in the crossbar. Said stem is provided with screw threads and carries nuts 62 firmlygripping the cross bar on both sides. The tuning fork is thus held in ahorizontal position in substantial parallelism to the key 40 above it.It is tuned to the tone corresponding to the key with which it isassociated.

It will be understood that a tuning fork is used in order to produce theoscillation which corresponds to the desired tone. Instead of atuningfork a reed .may be used which is tuned to the corresponding tone,and which has to be mounted in such a way that the oscillation is notdeformed or influenced by the fixation means, and that the oscillatinglength is well defined. This may be 4 accomplished by mounting itbetween two cross bars.

The tuning fork is best made of metal, but is not magnetized.

The tuning fork 60, in order to make it oscillate, is struck by a mallet1|] consisting of a spherical or cylindrical head 7| carried by an arml2. This arm is pivoted on a pivot pin 13 carried by an upright :56 orbetween two such uprights. The arm 12 has an extension M at the end ofwhich a counterpoise 15 is mounted which holds the said head against thelower surface of the key 48. The head consists either of soft materialor is lined with soft material. The counterpoise T5 is of such weightnot only to counterbalance the head but to impart to it a tendencytowards upward movement. The counterpoise, therefore, serves themultiple purpose of holding the head in the desired position of contactwith a key, of taking up some of the energy imparted to the head upondepression of a key and of breaking the downward movement of the head liwhen it has fulfilled its purpose. The latter effect may be obtained byarranging the stop 41 in such a way that it will act as a stop for thecounterpoise.

It will, therefore, be clear that upon depression of the key the head llwill strike shortly against the tuning fork 68 and will thus produceoscillations of the desired frequency.

A further part of the mechanical arrangement of the instrument consistsin the damping mechanism associated with the rear section 50 of the keyAd. This mechanism comprises the damping pad W5 consisting of leather,sponge rubber or similar relatively soft materiaL'pressed against thetuning fork. This pad is merely removed when the tuning fork is struckby the mallet. The damping pad is fixed on a head 77 mounted on an arml8 whose fulcrum 79 may for instance be formed between points or knifeedges (not shown) within a hole, recess or cut portion of the cross bar53. The outer end 80 of the arm carries a pin 8| sliding within a slot82 of a link 83 pivoted at 8 to the key section 50.

It will be manifest that when the key 40 is depressed and the tuningfork is struck by the mallet the rear section 50 moves upwardly and thelink 83 will lift pin 8| and the end 80 of arm 18 and will thereby lowerhead 11 and move it away from the tuning fork 6|).

A damping pad lifter 85 is moreover provided in the chest whichcomprises a cross wire 86 passing below the ends 8|! of the arms 18, andwhich is capable of lifting said arms when operated. This cross wire issupported on depending arm sections 81 joined to horizontal sections 88,which are pivoted on a post depending from the top board of the closedchest section 4|. The other end of the horizontal section 88 ispivotally connected (at 89) with the core 9| of magnets 92, which areoperable by depressing the left pedal H5. It will be clear that only asmall number of magnets is necessary to operate the transverse wire orwires 86 which lifts all the arms 18 as soon as this pedal is depressed.The magnets in this case are energized, the cross wire or wires 86raises the ends of the arms 18 and removes the damping pads 76 from thefork Ell, the pins 8| moving within the slots 82 of the links 83 duringsuch action.

The arms 18 are either slightly weighted at or near the end 80 carryingthe pin so as to move downwardly with the link 83 after having beenlifted, or the pin 8| is inserted into the slot 82 with some frictionwhich is suflicient to produce a downward movement of the arm whichapplies the damping pad 16 when link 83 moves downwardly, while thisfriction is easily overcome by the pull of magnet raising the cross wireor wires 86 by means of lifting levers 85. It will thus be clear thatthe two mechanisms for lifting the arms 78 are capable of independentaction. It will also be clear that these mechanisms permit holding andtransportation of the chest without requiring any adjustment.

The electrical arrangement includes the tuning fork 60 one prong ofwhich forms one plate of a condenser I00, while the second condenserplate is formed by a member 99 which is mounted on the board 53. Thissecond member 99 consists mainly of a strip of metal facing preferablythe inside of the prong.

It will be understood that the length of the strip 99 which determinesthe capacity of the condenser Hi will have to be adjusted in accordancewith the frequency, such adjustment depending to a large degree on thewidth of the prongs on the tuning fork, and on other circumstances. Itis preferable to arrange the strip 99 between the prongs of the tuningfork 60 because it is a well known fact that the vibrating prongs whenstruck'hard have a tendency to spread, and this would lead to a strikingof the prongs against the plate 99, which is to be avoided.

The condenser I00 formed between the prongs and the member 99 isconnected with a so-called padder formed by a small adjustable condenserIlll provided with means for adjusting the capacity of the circuit. Bymeans of a lead 94, these condensers are connected with the grid Ifll ofa I-IF oscillator Hi2 which is of any well known type and connected andoperated in a well known manner. The HF oscillations produced in theoscillator are modulated by the oscillations produced in the circuit 94,95, 99, BI] in a Well known manner. The connections shown correspond toone of the customary methods of operating and modulating an oscillatorand are not part of this invention. Any well known method will producethe same result and it is deemed unnecessary to describe or show thesewell known oscillator arrangements in detail.

In certain cases the metal strip H2 may be made of a thicknesscorresponding tothat of the prongs of the tuning fork and it is thenplaced in front of the end ill of the prongs as shown in Figure 5 of thedrawings. The condenser is in this case formed by the two end faces ofthe prong and strip respectively, and is changed by the oscillations ofthe prongs. denser may be used if necessary to increase the totalcapacity of the circuit.

The tuning fork 60 is connected with ground I04 by lead 95, one of thescrews 62 serving as a binding post.

The modulated oscillations generated in the oscillator arrangement aretransmitted to an amplifier H6 which contains a demodulator and thenecessary number of audio amplifying stages. This amplifier is of theusual well known type. According to Figures 1 and 2 it is contained incase 25, but in the modification shown in Figure 4, the amplifier isarranged in the section II of the keyboard chest in the space beneaththe keys and between the magnets 92. It is preferable to arrange aplurality of amplifiers and oscillator units one for every octave or fora small number of octaves in order to fit the carrier frequency and theamplifier arrangement including the audio transformers to the range ofoscillations A parallel conw which forms the output of the correspondingsection of the keyboard.

The demodulator and amplifier arrangement is a conventional arrangementwhich needs no specific description.

The speaker may be arranged within the chest but it is preferably aseparate unit placed on the keyboard and emitting in the desireddirection.

The action of one of the pedals has already been described. The otherpedals H3 and H4 for decreasing or increasing the tone intensity areelectrically operated by either adding or switching off amplifier stagesor by switching in or out resistances in the audio circuits. Bothmethods are well known and do not form part of this invention. Theapplication is merely indicated diagrammatically.

Changes in the general construction and especially in the electric ormechanic equipment do not necessarily affect the principles on whichthis invention is based.

I claim:

1. Afoldable electro-acoustical musical instrument of the type having apiano keyboard, mechanical means associated with each key of thekeyboard for producing mechanical oscillations and means for convertingsaid mechanical oscillations into electrical oscillations, saidinstrument comprising an elongated chest of substantially flat prismaticshape divided lengthwise into sections along a transverse dividing line,subdividing the keyboard, said sections being hinged to each other alongthe transverse dividing line, said chest having a closed and an openportion, the latter carrying the exposed portion of the keys of thekeyboard and the aforesaid mechanical and electrical means associatedwith each key.

2. A foldable electro-acoustical musical instrument of the type having apiano keyboard, mechanical means associated with each key of the saidkeyboard for producing mechanical oscillations, means for convertingsaid mechanical into electrical oscillations, a damping device for eachof said mechanical means and means for operating the same, saidinstrument comprising an elongated chest of substantially fiat prismaticshape divided lengthwise into sections along a transverse dividing line,subdividing the keyboard, said sections of the chest being hinged toeach other along the transverse dividing line, said chest having aclosed and an open portion, the latter carrying the exposed portion ofthe keys of the keyboard and the aforesaid mechanical and electricalmeans associated with each key, said closed portion containingsubstantially the damping device operating means including the means toconnect them with the keys, and electromagnetic means housed in saidclosed portion for operating the damping device of all the keys incommon.

3. A foldable electro-acoustical musical instrument of the type having apiano keyboard, mechanical means associated with each'key of the saidkeyboard for producing mechanical oscillations, means for convertingsaid mechanical into electrical oscillations, a clamping device for eachof said mechanical means and means for operating the same, saidinstrument comprising an elongated chest of substantially flat prismaticshape divided lengthwise into sections along a transverse dividing line,subdividing the keyboard, said sections of the chest being hinged toeach other along the transverse dividing line, said chest having aclosed and an open portion, the latter carrying the exposed portion ofthe keys of the keyboard and the aforesaid mechanical and electricalmeans associated with each key, said closed portion containingsubstantially the damping device operating means including the means toconnect them with the keys, electromagnetic means housed in said closedportion for operating all the damping devices of all the keys in commonand operating means for said electromagnets, including a source ofcurrent, connecti-ng cables and a pedal provided with a switch,

the latter forming a separate unit connected with the foldable chest ofthe said connecting cables for operating the damping means from a pointoutside the chest.

4. A foldable electro-aooustical musical instrument of the type having apiano keyboard, mechanical means associated with each key of the saidkeyboard for producing mechanical oscillations, means for convertingsaid mechanical into electrical oscillations, a damping device for eachof said mechanical means and means for operating the same, saidinstrument comprising an elongated chest of substantially fiat prismaticshape divided lengthwise into sections along the transverse dividingline, subdividing the keyboard, said sections of the chest being hingedto each other along a transverse dividing line, said chest having aclosed and an open portion, the latter carrying the exposed portion ofthe keys of the keyboard and the aforesaid mechanical and electricalmeans associated with each key, said closed portion containingsubstantially the clamping device operating means, the latter includingmeans to connect the same with the keys, electro-magnets housed in saidclosed portion and operating the damping devices for all the keys incommon, a separate pedal block containing a pedal with a pedal switchforming a unit and operating means for said electro-magnets including asource of 8 current and connecting cables leading to said magnet foroperating the damping means from a point outside the chest.

5. A folclable electro-acoustical musical instrument as claimed in claim.1 comprising supporting feet for each section of the chest hinged tosaid section for a folding movement of the feet bringing them alongsidethe said section.

6. A casing for the transportation and reception of 1a foldableelectro-acoustical musical instrument as claimed in claim 5 said casingbeing divided into two compartments, means for amplifying and forconverting electrical oscillation produced in the chest into acousticaloscillations, said means being housed in one compartment of said casing,the said second compartment being adapted to receive the folded chest,spacing ledges in said second compartment for holding the folded chestwhen inserted at a distance from the wall of the casing, thus providinga further compartment for receiving the cables and the pedal block.

CHARLES C. BROWN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,027,475 Hanson May 28, 19121,663,238 Bilhorn Mar. 20, 1928 2,187,251 Severy Jan. 16, 1940 2,226,900Dickerson Dec. 31, 1940 FOREIGN PATENTS Number Country Date 423,121Great Britain Jan. 25, 1935 492,762 Great Britain Sept. 27, 1938

